Students who dropped out of college in the past decade cost the economy $4.5 billion in lost income and federal and state income taxes, the American Institutes for Research (AIR) said. The organization tracked 1.1 million students who entered college in 2002. Of those, 493,000 did not graduate within six years and lost $3.9 billion in income in 2010 alone. The lost income would have generated $566 million in federal income tax revenue and $164 million in state income taxes, AIR said.